One of the most basic of the tools used by the medical practitioner is the syringe. Perhaps best known as an instrument used with a needle to inject medicine into a patient, the syringe has also been found useful in a variety of other applications. For example, syringes are particularly useful in performing angiographic procedures.
Angioplasty is a procedure for reducing the blockage which may occur in blood vessels. Over time, blood vessels may become partially or totally blocked due to buildup of cholesterol plaque along the walls of the vessel.
One location where plaque buildup is particularly dangerous is within the coronary arteries. The coronary arteries are those arteries which supply oxygen-rich blood to the heart. Buildup of plaque within the coronary arteries, a condition commonly referred to as coronary artery disease, can cause serious chest pain--angina--and, if not treated, may eventually cause heart failure.
Coronary angioplasty involves opening these blocked coronary arteries by inserting a balloon-tipped catheter into the artery. The balloon is inserted by making an incision usually in the groin or arm. A catheter is then inserted in a blood vessel exposed by the incision and threaded into the coronary artery.
An x-ray sensitive dye is injected into the coronary artery to enable the clinician to accurately position the catheter in the blocked portion of the artery. The catheter is inserted along the artery until the section of the catheter on which the balloon is located is positioned along the blocked portion of the artery.
A fluid is injected into the catheter to inflate the balloon. As the balloon is inflated, the plaque is compressed thereby expanding the narrowed artery. The clinician then withdraws the fluid from the balloon catheter, causing the balloon to deflate. The balloon catheter may then be removed from the patient.
It has been found that a syringe provides an effective tool for the introduction of fluid into the balloon catheter. However, because the pressure within the balloon must be carefully controlled during the angioplasty procedure, typical syringes having a plunger which may be freely depressed into the barrel are inadequate for this application.
If the pressure within the balloon is too great, the balloon may burst, a circumstance which usually requires immediate emergency surgery to correct. Some prior art attempts at designing a syringe which provides greater control over the pressures achieved in the balloon include providing a syringe which incorporates a plunger which is threadably connected to the barrel. Thus, the plunger may be slowly threaded into the barrel, resulting in a more controlled introduction of fluid into the balloon catheter.
A serious disadvantage to such syringes is the inability to freely and rapidly move the plunger in and out of the barrel in sliding reciprocation. For example, a preferred method of deflating the balloon is to rapidly withdraw the plunger from the barrel to create a negative pressure thereby causing the fluid to exit the balloon in an attempt to equilibrate the pressure within the balloon catheter. Withdrawing the plunger gradually from the barrel of the syringe by "unscrewing" the plunger requires a great amount of time and, more significantly, results in reduced effectiveness in deflating the balloon.
In recognition of the desirability of a syringe having a plunger/barrel assembly capable of operating in both a free or freely reciprocating mode and a threaded or restricted mode, syringes have been developed which address this problem. Most such syringes employ a thread engagement mechanism on the barrel of the syringe which can be actuated to selectively engage and disengage the threads on the plunger.
When the thread engagement mechanism is engaged, the syringe is "locked" into a threaded mode so that free reciprocating movement of the plunger sliding within the barrel is prevented. In this locked position, the plunger may only be moved within the barrel by rotation--gradually screwing it into or out of the barrel.
A serious design flaw which exists in some syringes employing a thread engagement mechanism on the barrel of the syringe is that the syringe is awkward to use. When using the syringe, one must grasp the barrel with one hand an, depress the plunger with the other hand, taking care to steadily hold the syringe as the plunger is depressed. Depending on the location and direction of actuation of the thread engagement mechanism, it can be difficult to properly hold the syringe in a steady position and control the thread engagement mechanism at the same time.
An additional disadvantage to such syringes is that some prior art syringes require that the barrel of the syringe be aligned in a certain orientation before the thread engagement mechanism can be actuated. This makes the syringe more difficult to use because the user must first ensure that the syringe is properly aligned before actuating the thread engagement mechanism.
A potentially serious flaw exists in some syringe designs which incorporate a thread engagement mechanism which, when actuated, causes slight movement of the plunger. This movement of the plunger could cause an unwanted and potentially dangerous increase or decrease in the pressure within the balloon.
If the balloon were to be expanded beyond acceptable limits, the coronary artery being repaired might be expanded beyond its capacity to yield. Rupture of the coronary artery would require immediate emergency surgery to correct, and, depending on the severity of the rupture, might require immediate bypass surgery.
Many prior art syringes also suffer from the disadvantage that it is impossible to view the fluid within the syringe along its entire path into the balloon catheter. During angioplasty, it is important to prevent air bubbles from entering the balloon catheter. If an air bubble were to enter the balloon and the balloon were to burst, the resulting embolism could cause serious injury to the patient's heart and possibly result in the patient's death.
Apart from angioplasty, other medical applications also benefit from a "locking" syringe. For example, such a syringe could be advantageously employed in a biopsy procedure--removing a tissue or cell sample from a patient to be later tested and further examined in a laboratory.
Such a syringe could be utilized in this way to avoid having to subject the patient to more serious surgical procedures to obtain the sample. A needle could be attached to the syringe and inserted into the patient such that the end of the needle contacts the tissue desired to be sampled.
The plunger could then be rapidly withdrawn from the barrel of the syringe to create a negative pressure within the barrel of the syringe. The effect of the negative pressure would be to draw sample tissue into the needle. Utilizing a locking syringe enables the clinician to lock the plunger in this retracted position to preserve the negative pressure and free the clinician from having to hold the plunger in the desired position.
However, many of the problems and disadvantages discussed above with respect to angioplasty syringes also exist in syringes used for biopsy.
It will be appreciated, therefore, that what is needed in the art are methods and apparatus which may be used to inject a fluid under pressure and enable the operator of the syringe to maintain a significant degree of control over the pressures obtained.
It would be an advancement in the art to provide an apparatus and method for a syringe in which the plunger is capable of selectively operating freely with respect to the barrel and operating in a "locked" or threaded mode.
It would also be an advancement in the art to provide an apparatus and method for such a syringe which is not awkward to operate because of positioning of a thread engagement mechanism located on the barrel of the syringe.
It would be a further advancement in the art if such an apparatus and method could be employed with a syringe such that the syringe may be actuated between freely reciprocating mode and a threaded or restricted mode of operation irrespective of the orientation of the barrel of the syringe.
It would be yet a further advancement in the art to provide methods and apparatus for a syringe which would enable the syringe to be actuated between a free position and a threaded position without any movement of the plunger with respect to the barrel during such actuation.
It would be an additional advancement in the art if such a syringe and methods could be provided that would permit the user of the syringe to observe the existence of air bubbles within the syringe and along the path of the fluid being injected by the syringe.
The foregoing, and other features and objects of the present invention, are realized in the locking syringe disclosed and claimed herein.